The present invention relates to an intraluminal prosthesis having controlled expansion. More particularly, the present invention relates to a stent having controlled radial expansion in vivo to prevent trauma to surrounding tissue.
Intraluminal prostheses are medical devices commonly known and used in the treatment of diseased tubular organs, for example, to repair, replace or otherwise correct a defect in a tubular organ, such as a diseased blood vessel. One particular type of intraluminal prosthesis used in the repair of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract and bile duct, as well as in a variety of other applications in the body.
Stents are generally open-ended structures which are radially expandable between a compressed insertion diameter and an expanded implantation diameter. Stents are often flexible in configuration, which allows them to be inserted through and conform to tortuous pathways in the blood vessel. Such a stent is generally inserted in a radially compressed state and expanded either through a self-expanding mechanism, or through the use of balloon catheters.
Endovascular stents have become well received for the treatment of stenosis, strictures, and aneurysms in various blood vessels. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the vessel. Such implantation typically involves delivery by way of a catheter advanced through the vascular system to the area of implantation, at which point the stent is released from the catheter and expanded within the blood vessel. It is well known in the art to use a self expanding stent by delivering the compressed stent and then removing the binding support allowing the stent to expand its uncompressed, expanded diameter. It is also well known in the art to use a balloon catheter to expand the stent from an interior expansion position.
Radial expansion of such a stent is typically necessary in order to overcome the stricture-causing blockage to a vessel. Conventional deployment of self-expanding stents, however, typically involves expansion over a very short period of time following release of the stent from the catheter. Such expansion over a short time period can cause undue trauma to surrounding tissue, thereby creating damage which can reduce the effectiveness of the stent, resulting in excessive tissue growth and possible restenosis.
In order to overcome such deficiencies, U.S. Pat. No. 5,843,158 to Lenker et al. proposes a controlled expansion endoluminal prosthesis including a tubular frame stent and a graft, and further having a reinforcing element which limits expansion of the stent-graft at a predetermined expanded size. The reinforcing element can be included in either the stent frame or the graft liner. The ""158 patent also discloses that the reinforcing element may be frangible or expansible, which can break or deform under a threshold expansive force to allow further expansion of the frame.
U.S. Pat. No. 5,899,935 to Ding similarly provides for an outer reinforcing element that is deployed in a compressed configuration, and provides an outer expansion limit.
However, all of these techniques add additional materials to the prosthesis which remain in the body and add to the thickness of the stent or graft liner. Accordingly, it is desirable to design a stent graft with an outer expansive limit, and a slowed or gradual expansion to protect the luminal surfaces from undue trauma while eliminating the additional thickness of permanent outer structures.
The present invention is directed to an intraluminal prosthesis including a radially self-expandable intraluminal stent and a biodegradable constraining element which prevents radial expansion of a selected portion of said stent to a fully-expanded diameter. The biodegradable constraining element is capable of biodegrading in vivo over a predetermined period of time to permit radial expansion of the constrained portion of the stent to the fully-expanded diameter.
A method of deploying the prosthesis is also disclosed. The method includes placing the stent into the vessel, permitting the unconstrained portion to radially expand upon deployment, and further permitting the constrained portion to gradually expand over time as the constraining elements biodegrade. Such controlled, gradual expansion decreases the potential for trauma or shock to tissue, particularly tissue which is already compromised, which can be caused by sudden or immediate stent expansion common to self-expanding stents. This promotes the stent effectiveness and acceptance by the body.